As a conventional technique, an doppler ultrasonic flowmeter using the ultrasonic pulsed doppler method has been known as disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742.
The doppler ultrasonic flowmeter has a configuration wherein ultrasonic pulses are cast onto a measurement line within a flow tube, ultrasonic echo signals, i.e., the reflected-wave signals from suspended fine particles in a fluid flowing in the fluid tube are analyzed so as to calculate the flow of the fluid flowing along the measurement line based upon the positions and velocities of the suspended fine particles. The measurement line is formed by an ultrasonic-pulse beam cast from the transducer.
The doppler ultrasonic flowmeter may be applied to an opaque fluid and an opaque-fluid tube, as well as having the advantage of measuring the flow of a fluid flowing a fluid tube in a non-contact manner. Furthermore, the doppler ultrasonic flowmeter has the advantage of measurement of the flow-speed distribution of an opaque fluid and the flow thereof, e.g., measurement of the flow of liquid metal such as mercury, sodium, and so forth, as well as having functions for measuring the flow-speed distribution and the flow of a fluid flowing in the flow tube with measurement along the measurement line.
The doppler ultrasonic flowmeter has the advantage of detecting change in the flow-speed distribution over time along the measurement line formed by the ultrasonic pulses cast onto the fluid from the transducer, and accordingly, it is hoped that the doppler ultrasonic flowmeter can be applied to measurement of a transient flow of a fluid flowing through the flow tube, and measurement of the flow-speed distribution and measurement of the flow in a turbulent situation.
An arrangement example of the ultrasonic flowmeter described above is disclosed in Japanese Unexamined Patent Application Publication No. 2000-97742.
Measurement with a conventional doppler flowmeter requires a situation wherein a fluid flowing in a flow tube which is to be measured contains a number of ultrasonic reflectors such as suspended fine particles or bubbles, and such ultrasonic reflectors continuously flow along the measurement line (formed by an ultrasonic beam). If the fluid flowing along the measurement line formed by the transducer does not contain any ultrasonic reflectors, dead time occurs for measurement of flow-speed distribution of the fluid, leading to a problem of deterioration in precision of measurement of the fluid-flow speed and measurement of the fluid flow.
Furthermore, while the conventional doppler ultrasonic flowmeter has a configuration wherein ultrasonic echo signals, i.e., the reflected-wave signals from ultrasonic reflectors are analyzed through signal processing so as to calculate the fluid-flow speed or the fluid flow, the signal processing method for the conventional doppler ultrasonic flowmeter has the disadvantage that a number of ultrasonic pulses must be repeatedly cast onto the fluid for calculating a single fluid-flow-speed distribution. The conventional doppler ultrasonic flowmeter having a configuration wherein ultrasonic pulses are repeatedly cast onto a fluid has the disadvantage of low time resolution, e.g., around 10 msec at the best, leading to difficulty in precise measurement of the fluid flow in a situation wherein a transient flow or a turbulent flow occurs in the fluid flow in the flow tube.
The present invention has been made in order to solve the aforementioned problems, and accordingly, it is an object thereof to provide an ultrasonic flowmeter which allows precise measurement of the fluid flow with improved time resolution even if a transient flow or a turbulent flow occurs in a flow tube.
Furthermore, it is another object of the present invention to provide an ultrasonic flowmeter having a function for storing the positional data and the speed data of ultrasonic reflectors, thereby allowing precise measurement of the fluid flow even in a situation wherein ultrasonic reflectors discontinuously and intermittently flow along the measurement line in the fluid flow which is to be measured.